The invention relates to network Medium Access Control (MAC) protocols.
In a local area network (LAN), each node or station is assigned an address that uniquely identifies that station as a single point of physical attachment to the LAN. According to the IEEE/ISO/ANSI LAN architecture, this level of addressing is the concern of the Medium Access Control (MAC) sublayer. Thus, each station attached to a LAN must have a unique MAC address on that LAN. This addressing mechanism is used by the MAC sublayer to deliver each frame to the appropriate station or stations on the LAN. Each frame is formatted to include a destination address and a source address. The destination address identifies the station or stations to receive the frame. The source address identifies the station from which the frame originates. Current LAN standards allow MAC addresses to be either 16 bits or 48 bits in length. Many LAN implementations support some form of acknowledged service. When a frame is transmitted by a source station using an acknowledged service, the destination station returns to the source station a response indicating the success or failure of the frame transmission. Typically, the response also includes a source and destination address pair. In a shared medium access LAN environment, such as a Carrier Sense Multiple Access (CSMA) network, this response address information is used by the source station to determine the validity of the response, that is, whether the response belongs to that source station. Because this address information is required of every response, it represents a significant protocol overhead.